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Linear accumulation rates and dry-matter accumulation rates were determined using Cs-137 distribution in sediment cores from 98 coastal and open-sea stations from around the Gulf of Finland (the Baltic Sea). Results showed that the average linear accumulation rate varied between 0.05-1.94 (mean 0.60) cm a(-1) which corresponds to a dry-matter accumulation rate of 0.01-0.30 (mean 0.15) g cm(-2) a(-1). Accumulation rates were high in recent mud sediments, especially near river outlets. The highest rates were found at inshore stations near Kotka town. Peak Cs-137 activities in cores from the whole study area varied between 0.04-2.4 Bq g(-1) wet weight. The highest activities were found in areas most affected by fallout from the 1986 Chernobyl accident, and corresponded to the overall areal distribution of Cs-137 in the soil but the areal distribution of Cs-137 in the sediments was also caused by the discharge of sedimenting particulate material from land. Total Chernobyl fallout in the area was between 1.4-80.5 (mean 21) kBq m(-2). Mixing of sediment strata was considerable in the uppermost sediment layers of many soft sediments, as indicated by the width of the Cs-137 peak in the cores. The Cs-137 technique can be used successfully in the Gulf of Finland because of high radiocaesium activities and the high accumulation rates. With the data obtained, the suitability of the stations for chronological sampling and monitoring was evaluated, and several new sediment stations that could be used for monitoring were identified.